Absolute frequency measurements of the 2-0 band of CO at 2.3 μm; Calibration standard frequencies from high resolution color center laser spectroscopy

The absolute frequencies of 20 lines of the 2-0 band of CO near 4260 cm^?1 have been measured by heterodyne frequency measurement techniques. Eleven of the lines were measured by saturated absorption techniques which produced linewidths of about 3 MHz. New rovibrational constants have been fitted to these measurements. A table of calculated transition frequencies is given with estimated absolute uncertainties as small as 0.0000023 cm^?1 (70 kHz) near the band center. The pressure shifts of three lines have been measured and fall in the range from ?0.9 to ?3 kHz/Pa (?122 to ?400 kHz/Torr). It is suggested that the generally accepted frequencies of the 1-0 band of CO should be lowered by 7 MHz.     

Pion production of heavily ionizing particles from aluminum

Total cross sections for producing alpha particles in an energy range from 0.6 to 5 MeV and protons with equivalent energy losses have been measured for π meson beams incident on aluminum from 60 through 400 MeV. A simple in-beam measurement was accomplished by use of CR-39 track detector material. The large cross sections found indicate directly that an important means for energetic π mesons to induce damage in silicon semiconductor elements is by production of alpha particles, their subsequent energy loss in the material, and recoils of daughter nuclei.     

Static dielectric properties of polarizable Stockmayer fluids

The effect on the thermodynamics and distribution functions in including point polarizability in the Stockmayer fluid is evaluated. A large effect on the dielectric constant is found. As in the non-polarizable case, the single super chain integral equation gives dielectric constants in excess of the computed values except at low dielectric constants.     

The spectrophotometric determination of rhenium

Some 50 analytical reagents were briefly checked for use in the spectrophotometric determination of rhenium. Seven reagents were checked in detail and interferences were examined. The most promising reagents appeared to be I-phenyl-2-thiourea and I,5-diphcnylcarbohydrazide.     

The determination of gold by atomic absorption spectrophotometry

Gold can be isolated from most other elements other than the platinum metals by the extraction of iron(II) 1,10-phenanthroline tetrabromoaurate in chloroform. After isolation gold can be determined in the organic solvent by atomic absorption spectroscopy or colorimetrically by decomposition of the complex and determination of the iron by bathophenanthroline.     

Stable isotopes may provide evidence for starvation in reptiles

Previous studies have attempted to correlate stable isotope signatures of tissues with the nutritional condition of birds, mammals, fishes, and invertebrates. Unfortunately, very little is known about the relationship between food limitation and the isotopic composition of reptiles. We examined the effects that starvation has on delta13C and delta15N signatures in the tissues (excreta, carcass, scales, and claws) of six, distantly related squamate reptiles (gaboon vipers, Bitis gabonica; ball pythons, Python regius; ratsnakes, Elaphe obsoleta; boa constrictors, Boa constrictor; western diamondback rattlesnakes, Crotalus atrox, and savannah monitor lizards, Varanus exanthematicus). Analyses revealed that the isotopic composition of reptile carcasses did not change significantly in response to bouts of starvation lasting up to 168 days. In contrast, the isotopic signatures of reptile excreta became significantly enriched in 15N and depleted in 13C during starvation. The isotopic signatures of reptile scales and lizard claws were less indicative of starvation time than those of excreta. We discuss the physiological mechanisms that might be responsible for the starvation-induced changes in 13C and 15N signatures in the excreta, and present a mixing model to describe the shift in excreted nitrogen source pools (i.e. from a labile source pool to a nonlabile source pool) that apparently occurs during starvation in these animals. The results of this study suggest that naturally occurring stable isotopes might ultimately have some utility for characterizing nitrogen and carbon stress among free-living reptiles.     

Algorithmic dimensionality reduction for molecular structure analysis

Dimensionality reduction approaches have been used to exploit the redundancy in a Cartesian coordinate representation of molecular motion by producing low-dimensional representations of molecular motion. This has been used to help visualize complex energy landscapes, to extend the time scales of simulation, and to improve the efficiency of optimization. Until recently, linear approaches for dimensionality reduction have been employed. Here, we investigate the efficacy of several automated algorithms for nonlinear dimensionality reduction for representation of trans, trans-1,2,4-trifluorocyclo-octane conformation--a molecule whose structure can be described on a 2-manifold in a Cartesian coordinate phase space. We describe an efficient approach for a deterministic enumeration of ring conformations. We demonstrate a drastic improvement in dimensionality reduction with the use of nonlinear methods. We discuss the use of dimensionality reduction algorithms for estimating intrinsic dimensionality and the relationship to the Whitney embedding theorem. Additionally, we investigate the influence of the choice of high-dimensional encoding on the reduction. We show for the case studied that, in terms of reconstruction error root mean square deviation, Cartesian coordinate representations and encodings based on interatom distances provide better performance than encodings based on a dihedral angle representation.     

Amplification by optical composites

Optical amplification is demonstrated in waveguides of composite materials consisting of nanocrystals of Cr:forsterite or Cr:diopside embedded in a host polymer with a matching refractive index. Small-signal gains of 1dB / cm at lambda=1.23microm are reported.